Air conditioning system with reheating means



AIR CONDITIONING SYSTEM WITH REHEATING MEANS William L. McGrath, Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y.,. a corporation of Delaware Filed May 2, 1957, Ser. o. 656,600 1 Claim. CI. 62-11;

This patent relates generally to air conditioning systems. More particularly this invention relates to an air conditioning system equipped with means for reheating air that has been previously cooled below its dew point temperature so that. air having desired temperature and humidity characteristics is provided for circulation to an enclosure.

Still more particularly, this invention relates to a control arrangement for use with a refrigeration system employed in an air conditioning unit. The control system forming the subject of this invention is operable under certain temperature and humidity conditions to reheat air passing over the evaporator of the refrigeration system used in the air conditioning unit.

Usually in air conditioning units of the type known as room coolers, air in an enclosure such as a room is circulated over the evaporator of a refrigeration system,

embodied in the air conditioning unit. Operation of the.

refrigeration system normally is under the control of a thermostat disposed or positioned in the air stream entering the; unit prior to its passage over the evaporator. Air conditioning units equipped "with the control described are unable to provide comfortable air flow within the enclosure being served when the temperature of the air within the enclosure may not be above the cut out point of the thermostat but the humidity of the air within the enclosure is sufliciently high so that the occupants of the enclosure are uncomfortable. I

In the McGrath Patent No. 2,679,142 it is proposed that an arrangement be employed permitting the passage of hot gaseous refrigerant from the compressor directly to a portion of the evaporator for the purpose of reheating air flowing from the adjoining portion of the evaporator. Thus air within the enclosure which may have a satisfactory temperature is cooled below its dew point temperature so that moisture is precipitated from the air and is then reheated to elevate its temperature to its original satisfactory level. Air flowing from the evaporator under these circumstances may have substantially the same temperature of the entering airbut has a relative humidity substantially less than the relative humidity of the air entering the evaporator. This invention is directed to an organization of the type described above and includes a control arrangement, a portion of which regulates the passage of condenser cooling medium over the condenser coil so that when reheat is necessary the flow of medium over the condenser coil is either reduced or stopped, resulting in higher temperature refrigerant in the discharge line and consequently higher temperature refrigerant for delivery to the reheat unit, being either a portion of the existing evaporator or a separate coil.

The chief object of this invention is the provision of an improved air conditioning system wherein air leaving the evaporator is subject to the action of a reheat coil.

A further object of this invention involves the provision of a control for a refrigerationsystem of the type employed in air conditioning units wherein said control,

2 operative under those circumstances where the temperature of the air flowing over the evaporator of the air conditioning system requires reheat, regulates passage of the cooling medium over the condenser in such a manner that the temperature in the discharge line of the refrigeration system issnbstanti-ally elevated from that existing in the discharge line under normal operating conditions when there is no demand for reheat.

A still further object of this invention involves the provision of a control of a type under consideration wherein flow of the cooling medium over the condenser coil is reduced when the requirements of the system are such that dehumidification of the air being circulated-in the area being served by the air conditioner is required.

The chief object of the invention is attained by employing a heat transfer element adapted to receive hot gaseous refrigerant from the compressor and which is so arranged that air flowing over the'evaporator may have its temperature elevated by virtue of heat transfer action between the air and the element. Control means are provided for elevating the temperature of the hot gas emanating from the compressor when it is desired that the heat transfer element referred to above be utilized to heat the air flowing from the evaporator.

These and other objects of the invention will be appar-' out upon a consideration of the ensuing description and drawings in which:

Figure 1 is a diagrammatic view of a refrigeration system equipped with the invention; and

Figure 2 is a partial view of the system shown in Figure 1 wherein the control means are modified.

Referring to Figure 1 wherein afrefrigeration system of the type employed inan air conditioning unit is shown" Iv diagrammatically, compressor 11 extracts vaporou's 're-' fn'gerant from evaporator 16 and forwards it at a'higher temperature and pressure to condenser 12 through discharge line 13. The condenser is subjected to the cooling action of a fan and provides liquid refrigerant for flow to the evaporator 16 through line 15. Interposed in liquid line 15 are the capillary members 17 and 20. Fan 41 delivers air over the evaporator.

Under those circumstances where it is necessary to reduce the temperature of the air within the enclosure being served by the air conditioning unit for the purpose f of dehumidifying the air, means are provided for elevating the temperature of the air to its original'level. This is' accomplished in this invention through the use of coil 20' having a connection to the hot gas discharge line 13 through solenoid valve 24 and three-way valve 25. Coil 20' is likewise connected to the evaporator 16 through the restriction 21.

The refrigeration systemdescribed is equipped with a" control operable in response to the temperature and humidity of the air entering the evaporator. The control system includes two switches 30 and 32. Switch 30 is a single pole, double throw switch, the arm of which is re-v sponsive to the action of a device for detecting the moisture content of the air entering the evaporator. Devices of this type are generally referred to as humidistats.

and humidity are high so as to indicate the necwsity for cooling, to energize the motor controlling the compressor and to deenergize solenoid valve 24 controlling flow of hot gaseous refrigerant to the three-way valve 25. The

control likewise operates when the temperature is high;

and the humidity lowto energize the compressor while deenergizing the solenoid valve. Under these circu try Patented Nov. 29, 1960 v striction 121 to the, heat transfer. coil; and then; through: tl1e;.three-way-.valve25 to .thesuction line 18. It will beappreciatedthat restriction 21 issized with respect to restriction 20 so that the tendency. for refrigerant flowing through restriction 17 is to follow the path through evaporator 16.- Spring 29 maintains the .valve 25 in the.

position shown in Figure 1.

When the temperature is low and-the humidity high,

the control mechanism functionsto cause'the compressor to. cycle on and the reheat valve 25 is .actuatedas the solenoid 24 is energized and perrnitshot gaseous refrig erant to fiow from: line..13 through the three-way 'valve to the coil 20'. The control is further arranged so that the fan 40 is rendered inoperative as the circuit to the motor controlling the fan is interrupted. Refrigerant flows under these latter conditions throughthe solenoid valve forcing the valve body 25 in.three-way valve 25 to this upper position against the. action of spring 29. Hot gaseous refrigerant flows through coil 20 and is condensed by the cool air flowing off the evaporator 16. The condensed refrigerant flows through capillary 21 into the evaporator 16.

Considering the operation of the invention when the temperature and humidity of the air entering the evaporator under the influence of fan 41 exceed the predetermined low cut-out temperature of the thermostat, a circuit is completed through power line supply L1, the high contact H on thermostat 32, high contact H on switch 30, through the motor controlling operation of compressor 11,.to power supply line L2. The condenser fan motor is energized by virtue of the-circuit through power supply line .Ll, high contact on the thermostat to. the low contact .on the humidistat to the motor and line L2. of the power supply; When the temperature of the air entering the evaporator is high and the humidity is low as sensed by humidistat 30, the circuit energizing the compressor is the same as before and the circuit energizing the condenser fan is likewise the same as before, thus under both of the operating conditions mentioned above, heat exchange coil 20 functions to add additional surface to the evaporator 16.

When the temperature of the incoming air is below the cut-out point of the thermostat, but the humidistat 30 indicates that the relative humidity of the air being circulated through the evaporator is high, the following circuits are made. A first circuit energizing the compressor is made through L1, the high terminal of the humidistat, the motor controlling operation of the compressor and line L2. A second circuit is made energizing the solenoid valve 24. This circuit extends from the power supplied on one line L1 to the arm of the thermostat, the low'contact'L of the thermostat and through the coil controlling operation of the solenoid valve to line L2. Under these circumstances it is to be noted that the circuit controlling operation of the motor, controlling fan 40 is interrupted. It will be obvious that once the thermally controlled switch 32 moves from its high contact, the circuit through the motor controlling fan 40 is interrupted.

Referring to Figure 2, there is shown a modification of the invention. In this modification the fan 40 instead of being inactivated has the speed thereof reduced by completing a circuit through a high resistance element 35. Thus when the humidistat is sensing a condition indicating a high relative humidity, in addition to the circuit to the compressor, the second circuit is made from a switch arm through the high resistance element 35 to the low contact of the humidistat 30 through the fan motor controlling-fan 40.

It willbe appreciated 'thatunder those'circumstances where the temperature is below the cm-out point of the thermostat but the humidistat indicates. a relative hu-..

midity of a high degree existing in the air entering the evaporator, coil 20 is subjected to the flow of hot gaseous refrigerant from the compressor and the fan 40 controlling movement of air over the condenser is inactivated. Under these circumstances head pressure on the machine rises as vwelLas the, temperature .of the gas in the discharge line 13. Inasmuch as this. gas is being fed to the reheat coil, through operation of the solenoid valve 24- and the three-waywalve :25 it will be obvious that a refrigerant havingaarelatively high degree of heat is being supplied to the reheat portion of the refrigeration system. Under-these circumstancesa greater degree of effectiveness is obtained in the reheat coil. It will be appreciated that when the discharge pressure rises, a corresponding rise in evaporator pressure occurs. The elevated evaporator pressure prevents frosting of the evaporator.

In order that the head pressure developed as a result of the operation of the refrigerant system on the reheat cycle does not become excessively great, a pressure actuated switch 50 responsive to the pressure developed in the discharge line is shown. This switch completes a circuit through the fan motor when completed. This causes air to flow once again over the condenser to cool the same.

It will be understood that various modifications will suggest themselves to those skilled in the art without departure from the spirit of this invention. For .example, different arrangements for metering refrigerant from the high side to the low side of the system may be employed without departing from .this invention.

While I have described a preferred embodiment of my invention, I desire it to be understood that the invention is not limited thereto, since it may be otherwise embodied within the scope of the following claim.

I claim:

In an air conditioning unit including a compressor; a first heat transfer coil; means for supplying cooling medium to said first heat transfer coil to condense gaseousrefrigerant delivered thereto by said compressor; a second heat transfer coil for receiving condensed refrigerant from said first heat transfer coil, said second heat transfer coil being arranged in two portions, the first of which is connected to the suction of said compressor and thesecond of which may be alternatively connected to either the suction or discharge of the compressor; refrigerant expansion means for metering liquid refrigerant to each portion of the second coil so that liquid refrigerant from the first coil may be fed to both portions of the second coil when both are connected to the compressor suction or may be fed to the first portion and serve to provide a path of flow for liquid refrigerant formed in the second portion of said second coil when it is connected to the compressor discharge, means for connecting the second portion of the second coil alternatively with the compressor suction or discharge; and means for passing air in heat transfer relation with said second coil, control means for regulating operation of the means for selectively placing the second portion of the second heat transfer coil in communication with either the compressor suction or discharge, said control means including an electric circuit operative to connect said control means to a source of electrical energy, and to control operation of the means supplying cooling medium to the first coil, a first switch responsive to the temperature of the air supplied to the second heat transfer coil, a second switch responsive to the humidity of the air supplied to the second heat transfer coil, said switches being operable in response to a predetermined temperature and humidity value respectively such that upon detection of a temperature and humidity value of air supplied to the second coil in excess of' said predetermined values and upon detection of' a'temperature' in excess'of said predetermined value the control is operative to energize the means midity value in excess of the predetermined value the 6 control is operative to actuate the means connecting the second portion of the second coil and the compressor discharge to assure communication therebetween and to regulate the supply of cooling medium to elevate the temperature of the gaseous refrigerant flowing from the 10 compressor discharge.

References Cited in the file of this patent UNITED STATES PATENTS Van Deventer Nov. 8, Newton Apr. 2, Groat Oct. 12, Steelman Sept. 2, McGrath May 25, Kraft Apr. 16, 

